The present invention relates to a large-area liquid crystal display device for use in, for example, AV (audio-visual) equipment and OA (office automation) apparatuses.
In recent years, there is demand for large-area, light-weight, thin, low-power-consuming, high-definition display devices for use in OA apparatuses and AV equipment such as home-use televisions. In order to meet such demand, development of practical, large-area display devices, including CRT (cathode ray tube), LCD (liquid crystal display), PDP (plasma display panel), EL (electroluminescence) display, and LED (light emitting diode) display, are in progress.
Among these display devices, liquid crystal display devices have great advantages over other devices because the liquid crystal display devices can have an extremely small thickness (depth), consume low power, and achieve a full-color display easily. Thus, recently, liquid crystal display devices have been used in variety of fields, and there is great demand for a large-area liquid crystal display device.
However, the manufacture of a large-area liquid crystal display device have problems, for example, an abrupt increase in the ratio of defects such as disconnection of signal lines and pixel defects during manufacturing. Moreover, such an increase of defects leads to a rise in the price. In order to solve the problems, Japanese publication of unexamined utility model applications, No. 191029/1985 (Jitsukaisho 60-191029) and No. 32586/1989 (Jitsukaisho 64-32586) propose a structure of a liquid crystal display device in which at least one of a pair of substrates provided with electrodes is made of a piece of large substrate produced by connecting a plurality of small substrates side by side.
For example, FIG. 13 shows the structure of a liquid crystal display device proposed by the above-mentioned publication, Jitsukaisho 64-32586. According to FIG. 13, a large-area liquid crystal display device is produced by bonding a piece of large active matrix substrate 51 and a piece of color filter substrate 54 having electrodes together so that a liquid crystal layer is placed therebetween. The large active matrix substrate 51 may be formed by connecting four pieces of divisional active matrix substrates 51a to 51d side by side and end to end. On each of the divisional active matrix substrates 51a to 51d, a pixel electrode 52 and a TFT 53 as an active element are provided at each intersection of electrode wiring that is produced in the form of matrix by a plurality of scanning electrodes 55 and signal lines 56.
In general, in an active matrix type liquid crystal display device, a minute active element is formed for each pixel on an active matrix substrate. It i s extremely difficult to achieve a high yield of such an active matrix substrate if it has a large area. Therefore, with regard to productivity, it can be said that the above-mentioned publication discloses an efficient method of fabricating a large-area liquid crystal panel by producing active matrix substrates having active elements thereon as a plurality of small substrates, connecting the small substrates side by side to produce a piece of large active matrix substrate, and bonding the large active matrix substrate to a piece of large counter substrate provided with color filters.
Meanwhile, at present, 550 mmxc3x97650 mm is the maximum size of mother glass used in a production line of an active matrix type liquid crystal panel that is generally used as a monitor of, for example, note-book-type personal computers and desk-top-type personal computers. FIG. 14 shows a comparison of a 550 mmxc3x97650 mm mother glass and a display with a size (diagonal) of 30 inches (aspect ratio of 3:4). It can be understood from FIG. 14 that it is possible to produce, for example, active matrix substrates and color filter substrates of a size not greater than a display size with a diagonal of 30 inches, but physically impossible to produce active matrix substrates and color filter substrates with a display size greater than the 30-inch display size. Moreover, since the conventional production line is designed for the 550 mmxc3x97650 mm mother glass, a glass larger than 550 mmxc3x97650 mm cannot be used as the mother glass.
By the way, when producing a liquid crystal display device with a diagonal of 40 inches and the above-mentioned conventional structure by connecting two active matrix substrates together, it is preferred to use two pieces of about 29-inch substrate as the active matrix substrates, and one piece of 40-inch substrate as the color filter substrate. In this case, as described above, the 29-inch active matrix substrate can be produced easily using a conventional production line and mother glass, but it is impossible to produce the 40-inch color filter substrate. Therefore, in order to achieve the 40-inch liquid crystal display device, it is necessary to introduce a new color filter production line corresponding to a larger mother glass for the production of the 40-inch color filter substrate.
However, the production line of color filters usually requires a photolithography process corresponding to three colors, i.e., red, green and blue, of color filters. It is therefore necessary to newly provide all the manufacturing devices such as a color resist applying device, pattern exposure device, developing device, baking device, and transport device. Namely, considerable investment is required. Accordingly, like the above-mentioned conventional example, the production of a liquid crystal display device by connecting a plurality of active matrix substrates side by side was proposed for the purpose of providing a large-area liquid crystal display device at a low price. However, a liquid crystal display device having such a structure tends to be expensive.
It is an object of the present invention to provide at a low prices a liquid crystal display device by connecting a plurality of active matrix substrates side by side, without requiring a new color filter production line corresponding to a large substrate even when each active matrix substrate has a maximum area obtainable from a conventional production line.
In order to achieve the object, a liquid crystal display device of the present invention includes:
an active matrix substrate having electrode wiring produced in a matrix form by a plurality of scanning lines and a plurality of signal lines arranged to intersect the scanning lines, and a pixel electrode and an active element for driving the pixel electrode at each intersection of the electrode wiring, the active matrix substrate being a piece of substrate produced by connecting a plurality of divisional substrates side by side, each divisional substrate being provided with color filters corresponding to the pixel electrodes, respectively;
a counter substrate provided with a common electrode, the counter substrate being disposed to face the active matrix substrate; and
a liquid crystal layer placed between the active matrix substrate and the counter substrate.
In this structure, the active matrix substrate is composed of a plurality of divisional substrates, and each divisional substrate is provided with color filters. Thus, there is no need to mount color filters on a piece of large counter substrate that is disposed to face the active matrix substrate. Therefore, when an active matrix substrate having a maximum area obtainable from a conventional production line is used as a divisional substrate, it is not necessary to form color filters on the counter substrate of a larger size. Namely, there is no need to introduce a new color filter production line corresponding to the larger counter substrate.
For example, when two pieces of active matrix substrate having a diagonal of 29 inches and color filters are used as the divisional substrates and connected to each other to produce a liquid crystal display device with a diagonal of 40 inches, the color filters are produced by a conventional production line for producing the 29-inch active matrix substrate. Hence, unlike the production of a conventional liquid crystal display device having a counter substrate provided with color filters, it is not necessary to introduce a color filter production line using a large mother glass with a diagonal of about 40 inches. Namely, it is possible to use the conventional production line at most even when producing a 40-inch liquid crystal display device.
In this case, it is also necessary to form a common electrode over the substantially entire surface of the 40-inch substrate. However, the formation of such a common electrode is carried out by simply introducing a film deposition system like a sputtering device corresponding to a large substrate. The cost of introducing such a film deposition system is much less than the investment in the color filter production line.